Fluid-dynamic device

ABSTRACT

A fluid-dynamic device comprising a holder ( 41 ) which supports a body ( 42 ) around which a fluid is arranged to flow, where the fluid when flowing round the body exerts a force with a component which is directed across the fluid&#39;s direction of flow. The body ( 42 ) is made of a sailcloth or foil-like material, comprising two sail-cloth portions ( 45, 46 ) which are joined along two respective, mutually corresponding edges, which together form an upstream edge ( 43 ). The holder ( 41 ) has two connecting devices for securing the body ( 42 ) at ends of the upstream edge ( 43 ) and for tightening the sailcloth portions ( 45, 46 ) between them while exerting a force and a reaction force along a connecting line ( 49 ) extending between the connecting devices. According to the invention the sailcloth portions ( 45, 46 ) have upstream areas ( 50, 51 ) between the upstream edge ( 43 ) and the connecting line ( 49 ).

The invention relates to a fluid-dynamic device of the type specified inthe introduction to claim 1.

From the field of sailing boats a number of bodies of theabove-mentioned type are known which comprise two sailcloth portionsresembling conventional airfoil profiles in cross section. Theseprofiles cause the air force component across the direction of flow tobe greater than for a standard single sailcloth. In order to obtain asail with such a wing profile, highly complicated devices have hithertobeen employed including, e.g. a number of straps, walls, cords etc.extending between the sail portions. The known sails are thereforeexpensive, heavy and complicated, thus making a holder for the sail,i.e. both the standing and running rig, equally heavy and expensive,while the sail is awkward to use.

The object of the invention is to provide a device of theabove-mentioned type which is inexpensive, lightweight, of simple designand easy to use.

This object is achieved with a device according to the invention withthe characterising features indicated in claim 1. Characteristicfeatures of embodiments of the device for the invention will be apparentin the dependent claims.

The invention will now be described with reference to the figures whichschematically illustrate advantageous embodiments of the deviceaccording to the invention, where the body, for example, is a sail andthe holder is a rig on board a boat.

FIG. 1 is a view of a wing profile.

FIG. 2 is a perspective view of a single sailcloth portion, foil or thelike, which is rectangular in top view and is influenced by a stretchingor tensile force.

FIG. 3 is a perspective view of two sailcloth portions of the typeillustrated in FIG. 2, which are interconnected, each of the sailclothportions being influenced by a stretching force.

FIG. 4 is a perspective view of the double sailcloth or sailclothassembly illustrated in FIG. 3, which is supported by a holder, wherethe sailcloth, assembly forms a wing, and a fluid, e.g. air flowsagainst the wing at an angle of attack relative to the wing.

FIG. 5 is a perspective view similar to that illustrated in FIG. 4,where the sail assembly is triangular in a side view like a Bermuda sailand is supported by a holder, such as a mast mounted on a boat sailingon the port tack.

FIG. 6 is a perspective view similar to that illustrated in FIG. 5, butwhere the sail's position is illustrated by dotted lines when the boatis heading straight into the wind, and by solid lines when the boat issailing on the starboard tack.

FIG. 7 is a side view of a boat with a substantially triangular sailwhere a luff of the sail extends close against a heavily curved mast.

FIG. 8 is a side view of what is illustrated in FIG. 7, but where themast extends in a less curved manner.

FIG. 9 is a side view of a mainsail in a position where the sail's tackcorner is located at a distance from the mast, the sheet corner havingbeen tightened towards the free end of a boom.

FIG. 10 is a side view of a jib whose luff in a first positionillustrated by a dotted line extends for its whole length along theforestay, and in a second position illustrated by a solid line extendsat its lower portion at a distance from the forestay.

FIG. 11 is a side view of a triangular sail, e.g. a jib, whose luff andafter leech are suspended in a headboard and in the lower parts can bestretched downwards and released alternately, the rope connected to thelower end of the leech that is not stretched downwards acting as asheet.

FIGS. 12 and 13 illustrate two cross sections through respectiveembodiments of a body according to the invention.

The invention is based on knowledge of the fact that birds which areadapted to a life of essentially continuous hovering with the leastpossible consumption of energy, such as an albatross, which can soar forup to 1000 km during a 24-hour period, have wings with a wing profilesimilar to the profile 1 illustrated in FIG. 1.

This profile 1 resembles a standard airfoil profile, but is very heavilycurved and very thick at its front portion. The windward side of theprofile, i.e. the side facing the reader, is substantially symmetricalabout a vertical centre line M, apart from at the profile's frontportion, and the windward side's largest outward bend is located nearthe centre line M. The leeward side is clearly asymmetrical about thecentre line M. In the front portion a nose circle 10 may approximatelybe inscribed.

The invention is further based on the sequence or first effectillustrated in FIG. 2. In this figure a rectangular sailcloth portion 2is illustrated, which extends in a plane P. The sailcloth portion 2 hasa leading edge 3 and a trailing edge 4. At a distance from the leadingedge 3, the sailcloth is influenced by two opposite, equal forces K1, K2with a force line LV which extends parallel to the leading edge. Onaccount of internal sailcloth stresses S1, S2, S3, which have beencaused by the forces K1, K2, and have components extending across theforce line LV in a sailcloth area 6 between the force line LV and theleading edge 3, the sailcloth material is pulled towards the force line,thus causing a raising of the leading edge 3 and a curving of thesailcloth. A curve of this kind can be supported by a highly flexibleconnecting element such as a lath 5, which can be connected to thesailcloth. It may, for example, be connected to one of the sides of thesailcloth, be located in a pocket thereof and supported against endbottoms of the pocket, or it may be woven into or otherwise inserted inthe sailcloth, the batten 5 being relatively resistant to breaking. Bythis means the formation of more bends of the leading edge against theforce line may be avoided, the sailcloth area 6 being in the form of onesingle bend with regular curvature. The lath 5 may extend over only afront area of the sailcloth portion 2 or over its entire length,considered in the direction of flow.

A first effect of this kind can be reinforced, e.g. by a sailclothportion with a convexly curved leading edge which has been reinforced,e.g. by folding the leading edge or by a cord extending along it whichis fixed to the leading edge. This reinforcement can absorb a greaterpart of the tightening force and components of this part that extendacross the line LV attempt to pull the leading edge towards this line.

By providing an additional sailcloth portion 7 whose leading edge andtrailing edge are connected to the leading edge 3 and the trailing edge4 respectively of the sailcloth portion 2, and stretching the sailclothportions 2, 7 as illustrated in FIG. 3, a sailcloth assembly can beobtained where both sailcloth portions 2, 7 are curved to the sameextent towards each other, thus forming a front, curved sailcloth area9. This sailcloth assembly 8 therefore has a cross section approximatelyin the form of a symmetrical airfoil profile. From FIGS. 2 and 3 it willbe seen that the length of the area 6 of the sailcloth portions 2, 7located in front of the force line LV may approximate to at least afourth of the circumference of the nose circle.

A body or sailcloth assembly 8 of the type illustrated in FIG. 3 may bemounted in a holder 11 as schematically illustrated in FIG. 4, where acouple of opposite tightening forces K1 and K2 are exerted by portions12, 13 of the holder against the sailcloth assembly 8 at its leadingedge. These forces are transferred to the respective sailcloths viasuitable means, such as reinforcing pieces or the like which, e.g. aresewn into the sailcloth portions. Other holder portions 14, 15 may bearranged mainly only for support of the sailcloth assembly at itstrailing edge 4. A fluid flow may flow against the sailcloth assembly 8with a velocity V at an angle relative to an extension C of a wingprofile chord. The sailcloth portion 7, i.e. the sailcloth portion onthe windward side of the profile according to the figure, is therebyinfluenced by fluid at a raised pressure and pushed in a directiontowards the sailcloth portion 2 located on the leeward side. Fluid at agreater velocity than the velocity V flows past the sailcloth potion 2on the leeward side of the profile, thereby causing it to be sucked awayfrom the sailcloth portion 7. Thus by merely tightening the sailclothportions in the above-mentioned manner and by the influence of the winda sailcloth assembly is obtained with a highly curved profile similar tothat illustrated in FIG. 1.

Due to a second effect, viz. that the fluid flow attempts to push theleading edge 3 in the downstream direction, the front sailcloth area 9is compressed, thus further increasing the thickness of the wingprofile.

A body or sailcloth assembly comprising two triangular, similarly shapedsailcloth portions is illustrated in FIG. 5, this sailcloth assemblybeing approximately in the form of a pointed bag. The end that forms thetop or point of the sailcloth assembly is attached by suitable means toa holder via a holding portion 16, and holding portions 17, 18 aresimilarly connected by suitable means to the respective corners of thesailcloth assembly at its leading edge 19 and its trailing edge 20respectively.

The holder may comprise a mast 25 and a boom 26 of a boat 27, theforward direction being indicated by F. The body or sailcloth assemblytherefore resembles a Bermuda sail and will hereinafter be called asail.

Air flows against the sail at a relative wind velocity V1 and at anangle of attack relative to a profile chord for the sail, and the boat27 according to FIG. 5 is sailing on the port tack.

FIG. 6 is a perspective view similar to that illustrated in FIG. 5, butwhere the sail's position is illustrated by dotted lines when the boatis heading straight into the wind, as indicated by the arrow V2, and thesheet is not tightened. The sail's position is illustrated by solidlines when the boat is sailing on the starboard tack and the winddirection is as indicated by the arrow V3.

When the sheet is not tightened and the sail can move freely, theprofile of the sail is symmetrical. Thus in the case of a boat which hasluffed into the teeth of the wind and no forces are exerted on the sailvia the sheet, a sail of this type shows no tendency to be pulled to thesides or to flap from side to side. It therefore remains substantiallyat rest with its centre plane parallel to the wind direction and in theposition illustrated by dotted lines in FIG. 6. This has been confirmedin practice and is a great advantage, since the boom also remains still.There is therefore no danger of people being hit and possibly pushedoverboard by a boom in motion, and the boat is easier to steer,particularly in a strong wind, e.g. when luffing to a buoy for mooring.It seems a likely possibility that the flapping of the sail in asidewise direction also results in a greater air resistance andconsequently a corresponding loss of height during tacking.

FIG. 7 is a side view of a boat 40 with a mast 41 supporting atriangular double sail 42 according to the invention, i.e. a sail withtwo overlapping triangular sailcloth portions. The sail has a luff 43and an after leech 44. According to the figure the mast 41 extends inthe space 39 between the sailcloth portions 45, 46 of the sail 42, butdoes not need to do so. In order to provide a variable tightening of themast so as to give it a variable curvature along the boat's longitudinalplane, a tightening line 49 is provided between an upper point on themast near the top 47 of the mast and a lower point 48 at the lower endof the mast 41.

In the position of the mast 41 and the sail 42 illustrated in FIG. 7,the line 49 is tightened to such an extent that the sail's leading edgeor the luff 43 is adapted to the curvature of the mast 41 and extendsalong it.

If the sail has this shape in an unloaded state and the sail is notloaded, the sailcloth portions 45, 46 will not bulge out, in which casethe sailcloth portions are located close together apart from in the areanear the mast where they extend round it. The sail thereby has a shapeapproximating that of a standard single cloth sail.

In the case of the relative position of the mast and the sailillustrated in FIG. 8, however, the line 49 has been slackened and themast has therefore straightened up. Thus its curvature has been reducedand the top of the mast has been raised a distance h. Since the sail'sleading edge previously extended along the more heavily curved mastaccording to FIG. 8, a front area 50, 51 of the respective sailclothportions 45, 46 of the sail is located in front of the mast 41 after themast has been straightened. A part of the tensile force originally borneby the line 49 has thereby been transferred to the sailcloth portions45, 46, since the force line for the force exerted against the sailclothportions extends between the upper end 52 and the lower end 53 of theluff 43, i.e. in this case near the line 49. The front areas 50, 51 ofthe respective sailcloth portions 45, 46 are thereby forced to assume acurvature and extend in a curved form towards each other, giving thesail a profile corresponding to a wing profile due to theabove-mentioned, first effect. Furthermore, the sail's leading edge ispushed backwards by the wind and the front area is further thickened dueto the second effect.

To assist in moving the front areas 50, 51 away from each other, thuspreventing them from extending in an undulating fashion during thetightening of the sail, connecting elements such as laths 54, 55 may beprovided to stretch out the sailcloth portions, i.e. they attempt tomove the luff away from a point located behind, e.g. the after leech,i.e. substantially along a wing profile chord. Connecting elements ofthe respective sailcloth portions may attempt to move the sailclothportions away from each other, and the connecting elements may, e.g., beelastically interconnected in pairs at the luff 43.

Elements of this kind may be provided on the sides of the sailclothportions facing each other, i.e. on the side facing in towards the space39 between the sailcloth portions, on the outside of the sailclothportions or in pockets provided in each sailcloth portion. The elementsmay be woven into or otherwise inserted in the sailcloth portions 45, 46or they may extend freely in the space 39 by being connected to thesailcloth portions at the latter's leading edge and behind it, possiblyat the trailing edge of the sailcloth portions. The elements preferablyhave so little rigidity that they do not need to be removed even thoughthe sail is reefed by being wound up on, e.g. the mast. The connectingelements 54, 55 may extend over only the front sail areas 50, 55 orcontinue towards or extend all the way to the trailing edge 44. Acombination of such connecting elements may be provided.

In each of the sailcloth portions 45, 46 and, e.g. near the luff, theremay advantageously be provided at least one admission opening 56, 57 foradmitting air from the side of the sail which momentarily forms theoverpressure side, i.e. the windward side of the sail, thus enablingthis air to help to keep the sailcloth portions 45, 46 apart from eachother. At least one discharge opening 58 may also be provided, e.g. atthe after leech 44, for discharging air from the space 39 between thesailcloth portions. On the inside of the openings 56, 57 at the luff andpossibly also the opening 58 at the after leech, there may be providedflap valves or the like (not shown) which may be variable, thusproviding valves that offer the possibility of varying the air pressurein the space 39 between the sailcloth portions 45, 46. The openings 56,57 may, e.g. act as non-return valves which let air in but not out,where the flaps can be moved towards or away from the openings under theinfluence of a pressure differential over the openings. During anoperation of the device according to the invention, air can therefore,e.g., flow freely into the body through the openings arranged on thesailcloth side which momentarily is the windward side (the overpressureside), while the openings arranged on the leeward side (theunderpressure side) are closed. Excess air in the body may bedischarged, e.g., through the opening 58 at the after leech.

The admission opening is preferably arranged and formed in such afashion that it can maintain its function even though the sail is reefedby being partially wound up on the mast. This can be achieved, e.g., bythe admission opening being elongated in a direction across a wind-upaxis, as indicated in FIG. 8. The discharge opening at the sail'strailing edge may be formed by the sailcloth portions here beinginterconnected apart from at the location of the discharge opening.

The sailcloth portions 45, 46 may instead be sealingly interconnectedalong all outer edges, not including any openings of the above-mentionedtype. In this case the inner space 39 may instead be arranged to beconnected to the surrounding air via at least one stop valve 59 which isonly schematically illustrated. Before a tightening of the sail 42, thestop valve 59 may be open. During a tightening of the sail, therefore,air can flow into the space 39 via the stop valve 59 in order to permita movement of the sailcloth portions away from each other. When thesailcloth portions have reached their desired final position, the valve59 can be closed, whereupon the volume of the space 39 is maintainedwhen sailing.

In order to facilitate a reefing of the sail by winding it up on themast, it is advantageous for the laths to extend at an acute anglerelative to the mast's longitudinal direction.

The sail may comprise a suitable combination of laths 54, 55, a valve59, openings 56, 57 and/or the opening 58.

The two sailcloth portions need not be similar in shape. Thus the sailmay comprise a first and a second sailcloth portion, where the firstsailcloth portion is narrower than a second, considered in the sail'schord direction. According to FIG. 8, therefore, the trailing edge ofthe first sailcloth portion may extend along a dotted line 60. Adischarge opening 58′ may then be formed by the trailing edge of thefirst sailcloth portion being sealingly connected to the secondsailcloth portion apart from at the location of the discharge opening58′.

FIG. 9 is a side view of a mainsail 72 with a luff 73 and an after leech74. The sail is double, comprising two sailcloth portions 75, 76 in thesame way as the above-mentioned sails. The sail 72 is held by a mast 77and a boom 78, where, e.g., a leech rope of the sail runs in grooves inthe mast and the boom. By means of cords or the like, a tack corner 79can be moved along the boom 78 between a front location 81 near the mast77 and a rear location 82 at a distance from the mast 77.

The mast 77 has only a small curvature. If the tack corner 79 is at thefront location 81, the force line for a force exerted between aheadboard 83 and the tack corner 79 therefore extends substantiallylinearly and near the luff. Thus no bends or only a small bend isessentially formed in the front portion of the sailcloth portions 75,76.

However, if the tack corner 79 is pulled backwards to the rear location82, the force line 84 extends for a greater distance from the luff 73and bends may be formed in the front area of the sailcloth portions, sothat the sail's profile can assume the shape of a wing profile asexplained above. The sheet corner 85 can also be pulled backwards tohelp with adjustment of the bending.

If the leading edge of the sail is convex in the forward direction andhas a greater curvature than the mast when the sail, e.g., is only lyingunfolded on a flat floor, the mast will exert a force in its transversedirection against the sail when the sail has been hoisted without havingbeen tightly stretched, the effect hereby created by the mast resemblingthe above-mentioned second effect, which is created by wind and whichattempts to make the sail's leading edge blunter. When in addition thesail is tightened, it is exposed to both the first and the secondeffect, with the result that the front area of the sail's wing profilebecomes very thick.

With an increase in wind the mast will become increasingly curved in theknown manner, thus extending forwards in a more noticeably convexfashion. The sail will thereby be influenced to a lesser extent by themast and assume a flatter form, which is advantageous in a strong wind.

Possible cross sections of the sail at different heights of the sail areindicated in the figure. In addition, cross sections are indicated whenthe boat (not shown) on which the sail is mounted is sailing on the porttack or starboard tack, or is luffed into the wind.

If there is mounted in the upper part of the mast an upper boom which isrotatably connected to the mast like the boom 78, and which can be heldprojecting out on the mast 77, the headboard 83 can be supported by theupper boom, and the headboard 83 and the adjacent, upper portion of theluff can be moved from or towards the mast in the same way as the tackcorner 79 and the portion of the luff near it. Instead of the sail beingtriangular and its upper end pointed, the upper edge of the sail can beadapted to the length of the boom, with the result that it may, e.g., betrapezoidal, rectangular or the like. With sails of this kind, moreover,a tightening device may be provided at the upper boom for the upper,front corner and possibly the upper, rear corner of the sail, thisdevice being of similar design to the tightening device for the tackcorner 79 and the sheet corner 85, and capable of being operated fromthe boat deck. The force line for the tightening forces may be caused toextend, e.g., at regular intervals from the mast.

The device for moving the tack corner 79 and possibly similarly theupper, front corner of the sail may provide control of wrinkling andbellying of the sail at the mast, also for a single cloth sail.

FIG. 10 is a side view of a jib 92 whose luff 93 is attached to aforestay 97 and whose after leech 94 runs freely. The jib has twosailcloths 95, 96 like the above-mentioned sails.

The jib 92 is illustrated in two positions, viz. a first position, wherethe jib is indicated by solid lines, and in a second position, where thejib is indicated by dotted lines. In the second position the jib 93extends for its entire length along the forestay, a lower end 98 of thejib 93 being located close to the forestay 97. In the first position thelower end 98 and the upper end of the luff are located at a distancefrom the forestay 97.

As will be understood from the above, the front portion of the jib 92will be curved and the jib's cross section will assume the shape of awing profile when a force line 99 for a tightening force exerted betweenthe lower end 98 of the luff 92 extends at a distance behind the luff92.

In this figure there are also depicted different jib cross sections ofthe jib when the boat (not shown) on which the jib is mounted is sailingon the starboard or port tack respectively and luffed into the wind. Inthe latter case the cross section is symmetrical.

The bottom of the forestay may be connected to the boat via a device 100whereby the jib can be rolled up on the forestay 97 for reefing the jib.

By slackening the forestay, the object may be achieved of causing it toextend concavely, viewed in the forward direction. The sail may therebyassume the shape in cross section of a wing profile which is thickenedat the leading edge, also in the case of sails whose leading edge in anunloaded state extends rectilinearly.

FIG. 11 is a side view of a triangular sail 102 with two sailclothportions 105, 106 like the above-mentioned double sails. The sail 102has a first edge 103 and a second edge 104. The sail is stretched at itscorners, where forces are exerted as indicated by the arrows K1-K4, theforce K1 and its reaction force K2 being exerted along a first forceline 125, and the force K3 and its reaction force K4 being exerted alonga second force line 126. The sail 102 is arranged to be brought into afirst air flow with a relative wind direction V4 or a second air flowwith a relative wind direction V5. The force line 125 is locateddownstream relative to the first edge 103 when the sail is brought intothe first air flow. The force line 126 is located downstream relative tothe second edge 104 when the sail is brought into the second air flow.

Near its upper corner, i.e. the corner which in the figure faces awayfrom the reader, the sail 102 may have an eye 111 or the like via whichthe forces K1 and K3 can be transferred to the sail 102 from a holder(not shown).

In order to exert the forces K2 and K4, the sail 102 may have lines 112and 114 respectively which are indicated by dotted lines.

When the sail 102 is brought into the first air flow and forces K1 andK2 are exerted, the line 112 acts as a downhaul line or a short forestayfor continuous tightening of the sail 102, and the line 114 acts as asheet.

At the first edge 103 which hereby forms an upstream edge, therefore,areas of the sailcloth portions 105, 106 according to theabove-mentioned first effect are moved away from each other and curvedin such a manner that the cross section of the sail resembles the crosssection of a wing.

On account of the above-mentioned second effect, the fluid flow alsoattempts to force the first edge 103 in the fluid flow direction,thereby as an additional effect attempting to make this blunter inshape, i.e. move the sailcloth portions 105, 106 further from each otherin the front sailcloth area, with the result that the wing profile hereobtains a further increase in thickness, which is advantageous. Thefirst edge 103 will hereby be slightly straightened, with the resultthat it extends closer to the force line 125. A wing profile of thistype is indicated by reference numeral 116 where a boat (not shown) onwhich the sail is mounted, is sailing on the starboard tack. A profile117 is also depicted where the boat is sailing on the port tack and aprofile 118 where the boat is luffed into the wind respectively. When notension forces or wind forces are exerted against the sail, it has aprofile 119.

When the sail 102 has been brought into the second air flow and forcesK3 and K4 are exerted, the line 114 acts as a downhaul line or a shortforestay, and the line 112 acts as a sheet. The sailcloth portions 105,106 are thereby moved away from each other at the second edge 104.Profiles corresponding to the above-mentioned profiles while sailing ondifferent tacks are indicated by the reference numerals 121 and 122,while a profile that is obtained when the boat is luffed into the windis indicated by the reference numeral 123. The reference numeral 120indicates a profile for a sail which is not influenced by tension orwind forces.

FIG. 12 is a schematic illustration of a cross section through anembodiment of a body 141 according to the invention. The contour of thiscross section resembles the extremely advantageous wing profileillustrated in FIG. 1. The body has two sailcloth portions 131, 132whose trailing edges E1, E2 are interconnected. The sailcloth portion131 of the body 141 which according to the figure is located on thewindward side of the body 141 is substantially symmetrical about acentre line M and has its greatest outward bending or outward curvatureat this centre line M. The leeward sailcloth portion 132 is asymmetricalrelative to the centre line M and has its greatest outward curvaturerelatively far forward. From a point near the centre line to thetrailing edge, the two sailcloth portions may abut against each other,e.g. depending on the profile's curvature.

FIG. 13 illustrates a cross section through a second body 142 comprisinga windward sailcloth portion 133, and a leeward sailcloth portion 134.For comparison, the leeward sailcloth portion 132 according to FIG. 12is indicated by a dotted line.

By means of this body 142 according to the invention the trailing edgeE3 of the windward sailcloth portion 133 is connected to the trailingedge E4 of the leeward sailcloth portion at the ends of the body, i.e.,e.g., at the ends located at the upper and lower parts of a mastrespectively. The remaining trailing edge areas of the sailclothportions therefore have the possibility of sliding relative to andtowards one another in the event of wind load on the body from differentsides. Connecting devices may be provided to hold the sailcloth portionsagainst one another substantially without preventing them slidingrelative to one another, e.g. by their interconnection via elasticconnecting elements such as elastic bands. The rear end of the leewardsailcloth portion can thereby move from the point indicated by E4 to thepoint indicated by E4′, and the leeward sailcloth portion 134 can assumethe extremely favourable shape illustrated in FIG. 13. The object isachieved here that the length of the leeward side is increased relativeto the length the profile would have had if sliding of the sailclothportions relative to one another had not been possible.

The fluid-dynamic device according to the invention has been describedabove with the body and the holder in the form of a sail and a mast,boom and/or stay of a boat respectively, and where air can flow aroundthe sail.

It will be appreciated, however, that the device according to theinvention may be employed in connection with any kind of fluid andtogether with any kind of device, where the body is required to exert aforce with a component which is directed across or at an angle relativeto the fluid's direction of flow.

Thus the device according to the invention may, for example, be employedas wings for aircraft, particularly for very light aircraft. Each wingmay hereby be designed, e.g. like the sailcloth assembly illustrated inFIG. 9, where the holder is in the form of a projecting, cylindricalrod, protruding sideways from the vessel's hull and preferably extendinginto the space between the sailcloth portions. The rod is preferablyrotatable, thus enabling the sailcloth assembly to be rolled our woundup on the rod.

On start-up of the aircraft, the sailcloth assembly may be wound off therod, thereby giving the wing a maximum area. Even with a low relativeair velocity, therefore, the lifting force may be very great. When therelative air velocity gradually increases, the rod may be rotated andthe sailcloth portions wound up on the rod, thus reducing the wing areawhile maintaining the lifting force.

In order to increase the load capacity, the space between the sailclothportions may be filled with a gas which is lighter than air, e.g.helium.

A device according to the invention may also be employed, e.g., inconnection with a power station, where the sailcloth assembly may besails of, e.g., a windmill or blades of a turbine for exploitation of awater current such as a tidal current. In this context it may beadvantageous to employ a device according to, e.g., FIG. 11, where thesailcloth assembly can be adapted to water currents which at differenttimes of the day and night flow towards the sailcloth assembly inopposite directions. When winding up the sailcloth assembly, it can beadapted to different current velocities.

1. A fluid-dynamic device capable of being influenced by forcescomprising a body (8;42;72;92;102) around which a fluid is arranged toflow, which fluid when flowing round the body exerts a force against itwith a component which is directed across the fluid's direction of flow(V1-V5), where the body (8;42;72;92;102) is made of a sailcloth orfoil-like material and comprising two sailcloth portions(45,46;75,76;95,96;105,106) with a common upstream edge(3;43;73;93;103,104), the upstream edge (3;43;73;93;103,104) beingarranged to extend substantially across the fluid's direction of flow(V1-V5) when it is flowing around the body, and the body(8;42;72;92;102) is supported by a holder (11;41;77,78;97;112,114) withtwo connecting devices (12,13;16,17;111,112,114) which are arranged forconnection with the body (8;42;72;92;102) at respective ends of theupstream edge (3;43;73;93;103,104) and for tightening the sailclothportions (45,46;75,76;95,96;105,106) between them while exerting a forceor a reaction force along a connecting line, i.e. a force line(84;99;125,126) extending between the connecting devices(12,13;16,17;111,112,114), characterised in that the sailcloth portions(45,46;75,76;95,96;105,106) have respective upstream areas (6;9;50,51)extending between the upstream edge (3;43;73;93;103,104) and theconnecting line (84;99;125,26), whereby the upstream areas (6;9;50,51)are curved across the connecting line (84;99;125,126) when the force isexerted along it, and the sailcloth portions (45,46;75,76;95,96;105,106)define a space (39).
 2. A fluid-dynamic device according to claim 1,characterised in that at least one of the connecting devices(12,13,16,17;111,112,114) is mounted outside the space (39).
 3. Afluid-dynamic device according to claim 1 or 2, characterised in thatthe holder comprises a mast (11;25;41;77), which supports the connectingdevices (12,13;16,17).
 4. A fluid-dynamic device according to claim 3,characterised in that the mast may be elastically curved, whereby it hasan inherent tendency to be straightened up, thereby creating the forces.5. A fluid-dynamic device according to one of the preceding claims,characterised in that the sailcloth portions (45,46;75,76;95,96;105,106)are connected to connecting elements (54,55) which attempt to stretchthe upstream areas (6;9;50,51) in the direction away from downstreamareas.
 6. A fluid-dynamic device according to claim 5, characterised inthat the connecting elements (54,55) may be mounted outside the body(42;72;92;102), inside the space (39) in the body (42;72;92;102) and/orin the sailcloth portions (45,46;75,76;95,96;105,106).
 7. Afluid-dynamic device according to one of the preceding claims,characterised in that in the upstream areas (6;9;50,51) of the sailclothportions (45,46;75,76;95,96;105,106) there is provided at least oneopening (56,57) via which fluid can flow into but not out of the space(39) defined by the sailcloth portions (45,46;75,76;95,96;105,106).
 8. Afluid-dynamic device according to one of the preceding claims,characterised in that in a downstream area of the sailcloth portionsthere is provided at least one discharge opening (58,58′) via whichfluid can flow out of the space (39) between the sailcloth portions(45,46;75,76;95,96;105,106).
 9. A fluid-dynamic device according toclaim 7 or 8, characterised in that the size of the openings (56,57,58)is variable.
 10. A fluid-dynamic device according to one of thepreceding claims, characterised in that the body may be wound about anaxis along the upstream edge and the admission openings are elongated,extending in a direction across the axis.
 11. A fluid-dynamic deviceaccording to claims 1-6, characterised in that the space (39) is closedand the body (8;42;72;92;102) is provided with a stop valve (59) foradmission or discharge of air, and for closing the space (39).
 12. Afluid-dynamic device according to one of the preceding claims,characterised in that the body (8;42;72;92;102) is arranged so thatfluid flows round it from at least two opposite directions and comprisestwo opposite edges (103,104) which are arranged to act alternately as anupstream edge and a downstream edge, both edges being provided withconnecting devices (112,114).
 13. A fluid-dynamic device according toone of the preceding claims, characterised in that it is a component ofa boat (27;40), the holder comprising a mast (11;41;77,78;97;112,114) ofthe boat (27;40) and the body (8;42;72;92;102) being a sail.
 14. Afluid-dynamic device according to one of the claims 1-12, characterisedin that it is a component of a wind power machine, the holder(11;41;77;97;112,114) and the body (8;42;72;92;102) being components of,e.g. a windmill.
 15. A fluid-dynamic device according to one of theclaims 1-12, characterised in that it is a component of a hydraulicmotor.
 16. A fluid-dynamic device according to one of the claims 1-12,characterised in that it is a component of an aircraft.
 17. Afluid-dynamic device according to one of the preceding claims, where thebody's (8;42;72;92;102) cross section, when a fluid flows around thebody, is in the shape of a wing profile which at the upstream edge(3;43;73;93;103,104) has a nose, wherein a nose circle (10) isapproximately inscribed, characterised in that the length of theupstream areas (6;9;50,51), measured in the body's (8;42;72;92;102)cross section, approximates to a fourth of the nose circle's (10)circumference
 18. A fluid-dynamic device according to one of thepreceding claims, characterised in that the sailcloth portions aresubstantially similar in shape.
 19. A fluid-dynamic device according toone of the claims 1-17, characterised in that one sailcloth portion isnarrower than the other, considered in the direction perpendicular tothe upstream edge.